Visible crew/equipment: When moving into their apartment Patrick Swazye kicks the statue to make it swing so they can get it inside. As they are looking at the statue, two moving men cross in back of them carring a mirror and as they pass you can see the director and camera crew in the reflection.
Continuity mistake: When Kim is watching Edward cut the roses, in closeups she's quite close to the curtain, and it's hanging straight down. In the wide shot she's slightly further away, and the curtain is angled outwards because she's holding it back with her hand.
Revealing mistake: The Gremlin who throws the beaker full of acid has his arm operated by a stick, which is visible as he chucks the beaker. (01:08:05)
Continuity mistake: The telephone on Scrooge's desk briefly disappears after his maid delivers an invitation to the archaeological society ball. (00:19:05)
Continuity mistake: During the final battle between Boone and Decker, at one point, they are wrestling on a wooden bridge, and the board beneath Boone's head breaks in half and falls into the cavern below. (It is even highlighted in a very dramatic shot looking downwards over the whole cavern as it falls) Yet, a few shots later, the board has suddenly re-appeared beneath his head, unbroken.
Continuity mistake: Toward the end, when James Belushi swerves to miss his dog in the middle of the street he crashes his car into a parked car and then roll to a stop. Notice before the camera cuts to a frontal shot of the wrecked car, that there is a huge spider crack in the windshield, as if James hit it with his head. This huge spider crack then disappears once the camera cuts to the frontal shot and the windshield is in perfect shape. (01:33:45)